Description: Thallus crustose, episubstratic or rarely endosubstratic, continuous to rimose-areolate, thin to moderately thick, pale white to greenish grey, dull, smooth, epruinose, sometimes delimited by a dark prothallus. Apothecia lecideine, 0.3-1.5 mm across, with a black, flat to rarely convex, epruinose disc, and a thick, persistent, raised proper margin. Medulla I-. Proper exciple of radially arranged hyphae, darker brown in outer part, paler within, extending from the deep reddish brown hypothecium; epithecium brown, N-; hymenium colourless, 70-90(-100) µm high, strongly inspersed with oil droplets; paraphyses simple to moderately branched in upper part, the apical cells swollen, with a brown pigment cap; hypothecium brown. Asci 8-spored, clavate to cylindrical-clavate, the apical dome K/I+ dark blue with a pale, conical-pointed apical cushion (axial mass), the wall I-, but the thin outer gel I+ blue, Bacidia-type. Ascospores 1-septate, but sometimes with 2 additional false septa, soon brown, narrowly ellipsoid with pointed, paler ends, sometimes slightly curved, (12-)17-25(-30) x (5.5-)7-10(-13) µm, the wall thickened subapically, but not at septum, not ornamented. Pycnidia rare, black, globose, unilocular. Conidia bacilliform, straight, .5-9 x 0.7-1 μm. Photobiont chlorococcoid. Spot tests: K+ yellow, then sometimes brownish, C-, KC-, P- or P+ faintly yellow, UV-. Chemistry: atranorin, plus traces of fulgidin and fulgoicin.
Note: a holarctic, humid subtropical to southern boreal-montane lichen found on smooth bark in rather humid woodlands, especially in open beech forests of the montane belt. Some forms with pluriseptate spores from coastal Tyrrhenian Italy perhaps deserve further study: they might prove to belong to a distinct taxon, corresponding to Lecidea parasema sensu De Not., which has a different chemistry (Giralt & al. 2000). The species is included in the Italian red list of epiphytic lichens as “Near-threatened” (Nascimbene & al. 2013c).